1. Field of the Invention
The present invention generally relates to modified oxides, and more specifically, to a highly charged ion modified oxide device having tunable resistance, to a method of making the device, and to a specific implementation that operates as a magnetic field sensor.
2. Description of Prior Art
In any sensor device that relies on sensing changes in an electric signal, the electrical resistance of the device is of concern. In general, this concern increases as the size of the sensor is reduced. The electrical resistance of the sensor device changes as the size changes due to properties inherent in the sensor material. Thus, for such devices, there is a need to be able to control the device resistance in an effective, commercially viable manner.
Considering a specific field wherein this need is particularly acute, in magnetic multilayer systems the inability to achieve a specific device resistance can create problems. For example, there are electrical resistance problems associated with current perpendicular to the plane (CPP) magnetic sensors. State-of-the-art CPP type magnetic sensors produced by using metal-metal interfaces and metal-insulator interfaces have electrical resistances that are too low and too high, respectively, to be viable. In the former case, the resistances of the CPP sensor is much too small for use as a hard drive read head because of the metal-metal interfaces. On the other hand, in the latter case, magnetic tunnel junction (MTJ) devices have an unfavorable impedance due to a complete insulating film that is part of its design, which leads to poor bandwidth.
Considering metal-insulator-metal (MIM) devices that can operate as magnetic sensors, magnetic fields are “sensed” due to a change in the completed device's resistance that is a fraction of the “base resistance”, i.e. the resistance of the device in the absence of a magnetic field. A change in the device resistance due to an external magnetic field is called “magneto-resistance” (MR). The quantitative value of the MR is typically determined by the ratio of the device resistance caused by an external field to the base resistance. For a MIM device to be technologically useful as a magnetic sensor, it must have both a desirable base resistance and also a “functional” MR. Depending on the specific technical details of the implementation, “functional” will depend on the quantitative value of the MR, as well as the linearity of the MR near zero external magnetic field and the rate of change of the MR near zero external field. As a consequence, demonstrating MR within a device that has a variable “base resistance” is highly desirable.